Tubes of the type having larger diameters at the base and smaller diameters at the top are often used for street lights, signs, etc. Many times, these are made from nested cylindrical tubes of varying diameters which nest within one another and are welded together at their junctions. These techniques are generally slow and expensive and require more metal than necessary for the proper strength. These operations require machinery which is both costly and space consuming.
Alternatively, tubular members are tapered to a variety of useful shapes by conventional swaging operations. In these operations, the uniform wall thickness of the tubular member is swaged to reduce the diameter of the member at selected portions with the consequent result that the wall thickness increases at the reduced diameter portion. The swaging process includes multiple steps which are different and separate from each other. An initial stock must be passed through the step-by-step procedures until it can finally be finished to a desired shape. The steps start with cutting a flat metal blank to a tapered shape, followed by forming it to a tapered tubing with the opposite longitudinal edges left unjoined together. Then, the next step causes the edges of the tubing to be joined together by means of a welding process. Any undesired portions that are present along the welded edges of the tubing are removed by means of a polishing or finishing process. The manufacture of such a product involves many steps, each including different processes. As a whole, a combination of these processes permits the manufacture of the product. However, it is a highly inefficient mass production technique. This swaging process also increases the manufacturing cost for each item.
Single-step swaging processes are also known, in which the swaging machine is specifically designed to provide a small-length tapered metal tubing (such as forks for bicycles). For long tapered tubes which are between 12 and 30 feet long, such as lighting standards, it is practically impossible to implement a single-step swaging process.
Another type of tube tapering machine has been devised wherein tubular metal stock is rotated about its longitudinal central axis. During this rotation, spinning rolls or shoes work on the exterior of the tube to deform it from its initial cylindrical shape to a smaller diameter of either straight or tapered shape. The surface presented against the work piece or tubular stock by the rolls or shoes tends to bend or flex the metal of the tube wall in a direction opposed to its circumferential curve or configuration. This flexing, which is repeated revolution after revolution of the tube, has a tendency to produce longitudinal cracks or to propagate insignificant scratches on the tube wall into cracks. This is particularly true on the inner surface of the tube.
U.S. Pat. No. 3,879,977, issued on Apr. 29, 1975 to F. B. Cauffiel, describes an apparatus and method for producing tapered poles. In this patent, the tapered pole is made from a particular tapered strip which is wound in a pseudo-helical manner on a tapered mandrel. Suitable means are provided for directing and guiding the strip on the mandrel such that the strip is wound from the small end of the mandrel toward the large end. Welding procedures are provided so that the edges of the strips can be formed together so as to produce a tapered pole.
U.S. Pat. No. 3,735,463, issued on May 29, 1973 to A. Merola, describes a method of forming tapered tubular members. In this method, a generally uniform wall thickness, hollow, cylindrical body is utilized as the starting material. The body is elongated by engaging the body at two spaced portions along its length. By applying a predetermined force to the body of the engagement portion, a substantial component of the force is directed parallel to the longitudinal axis of the body. When the body elongates between the engaged positions, the wall thickness of the elongated portion is reduced a predetermined amount. The process described in U.S. Pat. No. 3,735,463 was designed for the production of ball bats through a conventional type of swaging process.
U.S. Pat. No. 3,041,990, issued on Jul. 3, 1962 to C. K. Le Fiell, describes a tube tapering machine. This machine tapers tubes by using a tool which works on the metal of the workpiece to deform it. This tool is in the form of an annular ring presenting a concave surface or line of contact toward the convex surface of the tubular stock.
U.S. Pat. No. 4,622,841, issued on Nov. 18, 1986 to K. Yoshida, shows a single-pass swaging operation. In this patent, several swaging units are arranged in series in a tandem configuration. Each swaging unit includes a flywheel which acts as an anvil. It also includes a set of metal dies. In the tandem configuration, the die sets and the swaging units are arranged sequentially from one to another. On the entry side of the tandem configuration machine, a tubing stock of a prescribed length (which is to be tapered) is inserted, progressing through the machine toward the other side thereof. While the tubing stock is being fed forward, it is sequentially processed by the dies in the swaging unit that provide the tapered shape over the length. After having been processed through all of the dies, the stock is formed to a totally tapered shape.
U.S. Pat. No. 3,330,145, issued on Jul. 11, 1967 to G. F. Adolphi, describes a machine and method for tapering rod-like tubular workpieces. In particular, this patent describes the technique in which a cylindrical tube is gripped at both ends and a tension is applied axially to the tube. The tube does not rotate during the forming pass but is rotated at the completion of each pass. This device is generally intended for the manufacturing of tapered tubes having a diameter of less than one inch.
U.S. Pat. No. 5,315,854, issued on May 31, 1994 to the present inventor, describes a tube tapering apparatus having a variable orifice die. This apparatus has a frame, a tubing receiving end connected to the frame, a variable-orifice die arranged so as to be movable relative to the frame, and an axial tension cylinder connected to the tube receiving end so as to apply tension forces to the tube. The variable-orifice die includes a stand having a housing and a plurality of die segments arranged within the housing. The die segments contain a circular groove of varying radius. The die segments define an orifice having an entry plane and an exit plane. The exit plane and the entry planes are offset from the plane of rotation of the die segments.
Each of these prior art patents is designed so as to form a tapered tube whereby forces are applied to the exterior of the tube. As such, a relatively large diameter tube is cold-formed so as to have a wide diameter end that matches the original diameter of the tube and a narrow diameter end that is less than the original diameter of the tube.
Since the cost of the steel material used for the formation of such tapered tubes is of great importance in the manufacture of tapered tubes, it is important to be able to minimize the amount of material that is used for the tube. As such, under certain circumstances, it may be desirable to expand a relatively narrow diameter original tube so as to have a wide diameter that is greater than the diameter of the original tube. This reduces the cost of the material involved in the formation of the tapered tube.
It is object of the present invention to provide a tube expanding method and apparatus which increases the diameter of a tube via forces applied to the interior of the tube.
It is another object of the present invention to provide a method and apparatus for forming a tube which enhances the tensile integrity of the tube in the narrow diameter portion.
It is a further object of the present invention to provide a tube expanding device which minimizes the cost of materials for the formation of the tapered tube.
It is still a further object of the present invention to provide a pole that is formed by the tube expanding method and apparatus of the present invention in which minimizes undesired harmonic effects.
It is still a further object of the present invention to pole that is manufactured by the method and apparatus of the present invention which minimizes effective projected area while maximizing yield strength for the pole.
It is still another object of the present invention to provide a method and apparatus for the expansion of a tube diameter which is easy to use and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.